Production of nitrocellulose



Patented May 18, 1937 UNITED STATES PRODUCTION OF NITROCELLULOSE Milton 0. Schur, Berlin, N. H., assignor to Brown Company, Berlin, N. H.,

Maine a corporation of No Drawing. Application September 11, 1934,

Serial N0. 743,556 I 7 Claims.

This invention relates to the production of nitrocellulose and more particularly to nitrocellulose characterized by a low solution viscosity, i. e., the capacity of being dissolved in suitable solvent media to form solutions of low viscosity.

In my application Serial No. 461,854, filed June 17, 1930, now Patent No. 2,029,547, dated Feb. 4, 1936, I have disclosed a process of preparing nitrocellulose of low solution viscosity such as may 10 advantageously serve as the base in lacquer or film compositions. One phase of invention therein disclosed devolves about treating cellulose fiber more especially in interfelted or sheet form with dilute mineral acid solutions preparatory to ni- .5 tration. Another phase of invention therein disclosed involves treating the cellulose fiber with acid fumes or vapors, such as the fumes of hydrochloric and nitric acids, and then proceeding with.

the nitrating reaction. The present application is a continuation in part of the aforementioned application and is directed to that phase of in-- vention involving a pretreatment of the cellulose with acid fumes or vapors.

As pointed out in my parent application, an important advantage accruing from a pretreatment of cellulose fiber, more particularly in interfelted or sheet form with acid fumes or vapors, preferably the fumes or vapors of volatile mineral acids, is that not only is it possible to realize a marked lowering of the solution viscosity of the fiber but that mechanical loss of cellulose is minimized. Thus, when the pretreatment is carried out with acid vapors or fumes, there is no loss of cellulose such as tends to take place when the treatment is performed with aqueous solutions of chemicals; and when, in accordance with my invention, such pretreatment is applied to fibers in interfelted or sheet form and the sheet form is maintained through the nitrating operation, not only can the pretreated fibers be washed and dried, if desired, substantially without loss of cellulose, but the nitrating operation itself does not entail any serious loss of cellulose. In addition to maintaining the yield of nitration high, I gain importantly by my invention in the direction of preserving as part of the yield the nitrated fine fibers or fiber fragments, which, by virtue of their exceedingly low solution viscosity, contribute toward minimizing the solution viscosity of the ni- 50 trated product. Again, the mixed nitrating acid can be recovered from the nitrating operation at high efiectiveness for reuse, since the entrained or locked condition of the fine fibers and fiber fragments made possible by the interfelted cohesion of the other fibers means that only a com- Y paratively slight amount of colloidal and fine cellulose is picked up by the mixed nitrating acid during a nitrating operation.- I V While the principles of the present invention are applicable to cellulose fiber in such interfelted forms as tissue or paper, including small pieces or shreds of such forms and also shreds of lap stock or pulp-boards, they may be applied with especial advantage to pulp-boards, generally known as drier sheets. Wood pulp sheets, preferably such as are of high alpha cellulose content and otherwise suitable for use in the production of nitrocellulose, offers an important practical advantage when used as raw material. This advantage resides in the fact that chemical wood pulp mills are generally equipped to market, and in fact usually do market, unbeaten wood pulp in the form of drier sheets, which are produced by passing the processed wood pulp as an aqueous suspension over pulp driers sometimes built as large units capable of handling large amounts of pulp, say, two hundred tons or more of dry fiber per day. Such sheets are currently being sold, for example, for conversion into artificial silk by the viscose-rayon process, wherein they are handled as such with facility in making so-called alkali-cellulose, but they may be used to even greater advantage in nitrocellulose manufacture as hereinbefore described since they may be maintained in sheet form to the finished product, which, too, may be marketed as sheets. A specific example. of procedure falling Within the purview of the present invention may be carried out substantially as follows. Drier sheets of white, refined wood pulp of high alpha cellulose content, say,of an alpha cellulose content of at least about 93% and, say, about 0.035 inch thick, are suspended on a rack in a closed chamber which is charged with the fumes of hydrochloric or nitric acid admixed, if desired, with water vapor or steam. The exposure of the sheets to the acid fumes may be carried out for, say, one to two or more hours; and the atmosphere of acid fumes may be at a temperature ranging from room temperature to 100 C. or even higher. Indeed, the time and temperature conditions of the treatment with the acid fumes are subject to wide variation, depending upon the solution viscosity quality desired in the finished nitrocellulose. The acid fumes readily penetrate into and throughout the sheets so as to effect a substantially uniform chemical modification thereof. After the sheets have undergone the desired transformation in the atmosphere of acid fumes, they may be nitrated in any suitable mixed nitrating acid.

Preferably, however, the pretreated sheets are nitrated in two or more steps, as disclosed and claimed in my Patent No. 1,913,416, dated June 13, 1933. For instance, they may be initially immersed in a nitrating acid consisting of 17.0% H2O, 33.2% HNOa, and 49.8% H2804, at 45 C. This nitrating acid may then be drained from the sheets and a second nitrating acid, consisting of 17.5% H2O, 20.6% HNOb, and 61.9% H2804, at 40 C., may be added and the-sheets permitted to remain steeped therein for one hour. The second acid may then be drained from thesheets and the sheets drowned in water, washed, stabilized,

include so-called shredded pulp, which is obtained by taking relatively thick sheets of wetmachine undried stock or sheets of dried pulpboards and subjecting them to a tearing or shredding action, as in a cotton picker. The resulting shreds are comprised of interfelted fibers in the true sense of the word interfelted.

I claim:-

1. A process which comprises treating sheets of substantially unbeaten wood pulp with gaseous hydrochloric acid admixed with water vapor and then nitrating such treated sheets.

2. A process which comprises treating cellulose again Washed, and finally dried. As a result of fiber in interfelted condition with hydrohalide such practice, a satisfactory yield of nitrocellulose of low solution viscosity is realized, the results being far superior to those realized when cellulose in bulk form is similarly pretreated with acid fumes and then nitrated.

While it is possible to employ the fumes or vapors of various acids in performing the pretreatment of the cellulose accordant with my invention, nevertheless, I prefer to work with the fumes of mineral acids, particularly the volatile ones, such as hydrochloric and nitric acids, which are strong acids. Hydrochloric acid and its chemical equivalents, i. -e., the gaseous hydrohalide acids including hydrobromic, hydriodic, and hydrofluoric acids, are especially effective in the pretreatment, but hydrochloric acid is preferable in commercial practice by reason of its comparatively very low cost.

By the. expression "sheets, as used in the appended claims, unless I further characterize or qualify the sheets, I mean cellulose fiber in interfelted condition, irrespective of whether the sheets are of comparatively large area or have been cut into pieces of small size, as distinguished from pulp or cotton linters in bulk form, which latter when mixed with an aqueous medium results in a suspension of more or less individualized fibers. When small pieces of paper or drier sheets are used as raw material and are processed accordant with my invention, the nitrating procedure that I may follow may be more or less similar to that customarily employed in the industry. When using sheets of comparatively large area, such as drier sheets, however, I may to advantage perform the various treating steps of my process while the sheets are supported in frames or on racks or are suspended from rods or clamps. The sheets are preferably maintained in spaced parallel relation while they are undergoing the various treatments of my process, so that the reagents and wash water will contact substantially uniformly with all the surfaces presented by the sheets and thus ensure substantially uniform treatment thereof. By the expression cellulose fiber in interfelted condition, I intend to acidin gaseous form under time and temperature conditions to effect a marked lowering of the solution viscosity of the fiber; and nitrating the so-treated fiber in such interfelted condition.

3. A process which comprises treating cellulose fiber in interfelted condition with gaseous hydrochloric acid under time and temperature conditions to effect a marked lowering of the solution viscosity of the fiber; and nitrating the so-treated fiber in such interfelted condition.

4. A process which comprises treating cellulose fiber in interfelted condition with a mixture of water vapor and vapor of a strong mineral acid, such as hydrochloric, hydrobromic, hydriodic, hydrofiuoric, and nitric acids, under time and temperature conditions to effect a marked lowering of the solution viscosity of the fiber; and nitrating the so-treated fiber in such interfelted condition.

5. A process which comprises treating cellulose fiber in interfelted condition with vapors of a strong mineral acid, such as hydrochloric, hydrobromic, hydriodic, hydrofluoric, and nitric acids, under time and temperature conditions to effect a marked lowering of the solution viscosity of the fiber; and nitrating the so-treated fiber in such interfelted condition.

6. A process which comprises treating wood pulp in interfelted condition with vapors of a strong mineral acid, such as hydrochloric, hydrobromic, hydriodic, hydrofluoric, and nitric acids, under time and temperature conditions to effect a marked lowering of the solution viscosity of the pulp; and nitrating the so-treated pulp in such interfelted condition.

'7. A process which comprises treating cellulose fiber in interfelted condition for a period of one to two or more hours with vapors of a strong mineral acid such as hydrochloric, hydrobromic, hydriodic, hydrofluoric, and nitric acids, thereby effecting a marked lowering of the solution viscosity of the fiber; and nitrating the so-treated fiber in such interfelted condition.

MILTON O. SCHUR. 

